1. Field of the Invention
This invention pertains to an apparatus and method for separating gas mixtures by a pressure swing absorption system, and relates, more particularly, to the regulation of the work done by a compressor in moving a consumable gas to the absorption apparatus depending on the gas consumed by an end user by varying the valve timing that regulates the passage of pressurized air from the compressor to the absorption apparatus.
2. Description of the Related Art
Gas fractionalization systems are used for separating a desired gas from a gas mixture, such as air. A typical gas fractionalization system is an oxygen concentrator, which separates oxygen from air for subsequent inhalation by a patient. An oxygen concentrator, or similar pressure swing absorption system, typically includes molecular sieve beds for separating the gas into an oxygen and a nitrogen fraction, whereby the oxygen is subsequently provided to the patient while the nitrogen is retained in the sieve bed and subsequently purged. Generally, in a gas fractionalization system, two sieve beds are utilized. One sieve bed separates nitrogen from the oxygen while the other sieve bed is simultaneously being purged of the nitrogen previously absorbed during the prior separation cycle.
Typically, oxygen concentrators utilize a compressor that draws air from the ambient environment and presents the air to the molecular sieves for separation of the gases. A flow control device located between the molecular sieves and the patient controls the amount of oxygen delivered to the patient. Typically, an oxygen concentrator can provide a flow of oxygen ranging from 1 liter per minute to 5 liters per minute. A typical oxygen concentrator is illustrated in U.S. Pat. No. 5,183,483 the contents of which are incorporated herein by reference.
Even though oxygen concentrators are designed to provide an oxygen flow rate between 1 to 5 liters per minute, these concentrators are typically operated at less than full capacity and typically are operated to provide only 2 liters of oxygen per minute. While these oxygen concentrators may provide various flow outputs of oxygen, such systems are generally not designed to provide a varying input flow of air into the molecular sieves. Accordingly, the compressors of these systems continuously operate at one work level, which is that level required to produce the maximum flow of oxygen, e.g., 5 liters per minute. The result is that in a typical operation setting, e.g., 3 liters per minute, the compressor is needlessly working harder than required to produce the desired flow of oxygen selected by the patient. The drawbacks of the compressor working harder than necessary are that the compressor at full capacity is noisier than required and also utilizes more power than required. Thus, it is desirable to reduce the work of the compressor when the desired flow rate from the oxygen concentrator is less than the maximum flow rate that the concentrator can provide.
U.S. Pat. No. 4,561,287 (xe2x80x9cthe ""287 patentxe2x80x9d) discloses an oxygen concentrator system that automatically controls the valve timing to regulate the flow of pressurized air from a compressor into the molecular sieves. This is accomplished in the ""287 patent by monitoring the pressure levels within the product chamber and using the detected pressure to directly determine patient utilization, such as the flow of concentrated gas to the patient from the product chamber. However, the system taught by the ""287 patent has difficulty determining patient utilization, and, hence, accurately controlling the valve timing, because the measured pressure levels in the product chamber vary for reasons other than patient utilization. In particular, the present inventors noted that the pressure in the product chamber is a function of the valve pressurization time. Because different pressurization times for the molecular sieves result in different pressures within the product chamber, a system, such as that taught by the ""287 patent, which determines patient utilization directly from the pressure in the product chamber, will incorrectly determine that patient utilization has changed if the pressurization time has changed, even though the actual patient utilization remains unchanged. For these reasons, it is difficult, if not impossible, to control the valve timing in a reliable and stable manner based directly on the measured pressure in the product chamber. From the above-described problems with conventional oxygen concentrations systems, the present inventors determined that what was needed was a control system and method of interpreting the product chamber pressure is independent of the valve pressurization time to determine patient utilization.
Accordingly, it is an object of the present invention to provide a pressure swing absorption system wherein the operation of the compressor is modified to correspond with the desired output of the product gas resulting in a reduction in the power requirements of the compressor and that does not suffer from the disadvantages associated with conventional pressure swing absorption systems.
Furthermore, it is an object of the present invention to provide a gas fractionalization system having control system in which a parameter indicative of the flow rate of the product gas is utilized to vary the valve timing for communicating pressurized air flow from the compressor to the molecular sieve chambers, thereby reducing the power consumption of the system and providing a more tranquil operating environment.
These objects are accomplished according to the principles of the present invention by providing a gas fractionalization system having a control system for regulating the flow of pressurized air flow from the compressor to the molecular sieve chambers based on a ratio of pressures in the product chamber. More specifically, the gas fractionalization system of the present invention includes a compressor for receiving air from the ambient environment, a gas separation chamber for producing a concentrated gas portion from the air, a valve for presenting compressed air to the gas separation chamber at a duration of a pressurization time, and a product chamber for receiving concentrated gas from said gas separation chamber. The control system includes a pressure sensor for sensing the high and low gas pressures within the product chamber. A processor determines the pressure ratio of the high and low gas pressure within the product chamber, and a valve controller manipulates the valve to provide compressed air to said gas separation chamber at a pressurization time corresponding to the pressure ratio.
It is a further object of the present invention to provide a method of varying a valve cycle time to reduce the power requirements of a compressor in a pressure swing absorption system that does not suffer from the disadvantages associated with conventional pressure swing absorption systems. This object is achieved by providing a method that includes 1) determining a high pressure level of gas within a product chamber of a gas fractionalization system, 2) determining a low pressure level of gas within the product chamber, 3) calculating a pressure ratio of the high pressure mark versus the low pressure, and 4) manipulating a position of a valve that controls delivery of pressurized gas from a compressor to a gas separation system in such a gas fractionalization system based on the pressure ratio for controlling presentation of pressurized gas to the gas separation system during a charging phase.
These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.